Shaft positioning apparatus

ABSTRACT

Shaft positioning apparatus including a spiral cam in supporting relation to an interposer cam which, by moving perpendicular to the axis of the shaft, lifts the shaft from contact with a shaftsupporting and positioning stepped cam. The stepped cam and the spiral cam are mounted on a common drive member and have a substantially constant difference in radial length at any angular position so that the interposer cam can lift the shaft regardless of the orientation of the stepped cam.

[United States atent Patalki [451 May 23, 1972 [54] SHAFT POSITIONING APPARATUS 1,429,481 9/1922 Ayers,.lr ..74/567 FOREIGN PATENTS OR APPLICATIONS 917,383 9/1954 Germany ..74/567 Primary ExaminerMilton Kaufmann Assistant Examiner-Wesley S. Ratlifi, Jr.

Attorney-Charles C. English, Leonard Zalman and William E. Cleaver [57] ABSTRACT Shaft positioning apparatus including a spiral cam in supporting relation to an interposer cam which, by moving perpendicular to the axis of the shaft, lifts the shaft from contact with a shaft-supporting and positioning stepped cam. The stepped cam and the spiral cam are mounted on a common drive member and have a substantially constant difference in radial length at any angular position so that the interposer cam can lift the shaft regardless of the orientation of the stepped cam.

6 Claims, 2 Drawing figures INVENTOR ANDREW 8. PA 771K ATT NEY PATENTEUMAY 23 me SHAFT POSITIONING APPARATUS In computer systems utilizing a magnetic drum as the memory element, information is stored and retrieved by. positioning a transducer head mounted at the end of a shaft adjacent one of a plurality of tracks arranged along the longitudinal axis of the drum. The information storage capacity of the drum is determined primarily by the accuracy with which the transducer head can be positioned by the shaft adjacent a selected one of the tracks. To this end, closedloop servo systems and open-loop systems have been developed to control the movement of the shaft. Closed-loop servosystems are disadvantageous because these systems require the use of several rather costly feedback transducers and compensation networks to achieve accurate positioning of the driving mechanism for the shaft. Conventionalopen-loop systems are dissatisfactory because these systems require several parts which must satisfy close manufacturing tolerances.

Accordingly, an object ofthe present invention is to provide an improved shaft positioning apparatus.

Another object of the present invention is to provide a low cost shaft positioning apparatus.

A further object of the present invention is to provide a shaft positioning apparatus which is not dependent for accuracy on the exact position or orientation of the driving mechanism for the shaft-supporting member of the apparatus.

A further object of the present invention is to provide a shaft positioning apparatus which does not require several parts having close manufacturing tolerances.

In accordance with the invention the shaft positioning apparatus includes a spiral cam mounted on the drive shaft of a stepping motor, a stepped cam mounted on the drive shaft and secured rigidly to the spiral cam, a spring-loaded. shaft member normally having one end in contact .with a step of the stepped cam, and an interposer cam supported at one end'by the spiral cam and shaped such that movement in one direction lifts the shaft member from the step of the stepped cam. Lifting of the shaft member from the step of the stepped cam permits the stepped cam to rotate such that movement of the interposed cam in the opposite direction positions the shaft member on a different step of the stepped cam.

In a preferred embodiment of the invention, theinterposer cam has first and second horizontal sections and an inclined section. In this embodiment, the interposer cam moves in response to movement of the armature of a high speed solenoid.

For a better understanding to the invention together with other and further objects thereof, reference should now be had to the following detailed description which is to be read in conjunction with the accompanying drawing in which:

FIG. I is a side elevation view of an assembly embodying the shaft positioning apparatus of the present invention; and

FIG. 2 is a top view of the apparatus of FIG. 1, taken along line 22.

Although the shaft positioning apparatus of the invention can be used to position a wide variety of members, it is particularly useful in positioning the transducer head of a computer system. Accordingly, the invention is described in the environment of a computer system.

Referring to the drawing, a transducer head 10 is attached to a shaft member 12 by a linkage 14 which is biased by a spring 16 to maintain transducer head 10 adjacent a conventional magnetic storage drum l8. Transducer head 10 is connected electrically to suitable conventional apparatus (not shown) which either supplies electrical signals to transducer head 10 or receives electrical signals from transducer head 10. Drum 18 is characterized by a plurality of tracks (not shown) of information recorded magnetically around its periphery. To record information on or retrieve information from a selected track on drum l8, transducer head 10 is positioned, by movement of shaft member 12, in the manner described in detail hereinafter, adjacent the selected track.

A roller 20, carried by shaft member 12 at the lower end thereof, is maintained in contact with one of the curved steps 21 of a stepped cam 22 by a compressed spring 15 situated between shoulder 17 of shaft member 12 and a stationary structure 19. Cam 22 is carried by the drive shaft 24 of an appropriate conventional stepping motor 25, which in response to an appropriate signal supplied thereto, rotates shaft 24 and hencecam 22 in either a clockwise or a counter-clockwise direction. The number of steps 21 is equal to the number of recording tracks on drum l8 and the radial distance from the center 26 of shaft 24 to each adjacent step 21 differs by an amount equal to the spacing between those tracks. For example, if drum 18 has 50 tracks spaced four hundredths of an inch apart, cam 22 will contain 50 steps with the radial distance from center 26 of each adjacent step 21 differing by four hundredths of an inch. In this example each step 21 defines an angle 0 of 7.2.

Movement of shaft member 12 from one of the steps 21 to another of these steps is accomplished according to the invention by the interaction of an interposer cam 28 and a spiral cam 30. One end of cam 28 rests slidably on the spiral surface 31 of cam '30. The top surface of cam 28 includes a first horizontal section 32 having a height h,, a second horizontal section 34 having a height h and an inclined section 36. The bottom surface 38 of cam'28, the surface in sliding contact with cam '30, is parallel to sections 32 and 34. As clearly shown in FIG. 2, a portion of roller 20 is normally above section 32 of cam 28.

Cam 30 is mounted on shaft 24 and secured to cam 22 by, for example, bolts 39. The radial distance from center point 26 of drive shaft 24 to the spiral surface 31 of cam 30 changes at the same angular rate as the radial distance from point 26 to steps 2] of stepped cam 22. More particularly, for the example previously set forth, the radial distance from point 26 to the spiral surface 31 of cam 30 would change by about four hundredths of an inch for an angular rotation of about 7.2". Cams 22 and 30 are oriented on shaft 24 such that for any angle of rotationof these earns the height h,,, measured along the projected longitudinal axis of shaft member 12 is both greaterthan the sum of height h of section 32 of cam 28 and height h,,,, of cam 30 (also measured along the projected longitudinal axis of shaft member ,l2)and less than the sum of height h of section 34 of cam 28 and height h of cam 30.

The end of cam 28 remote from cam 22 is supported pivotally by a pin 40 secured to a rod 42 mounted to move on supporting bearings 44, which may be cylindrical rods or other guide'members. The armature 46 of a high speed solenoid 48, which also includes a stationary U-shaped iron core 50 and an energizing coil 52, is attached rigidly to rod 42. To maintain armature 46 remote from core 50 when coil 52 is not energized, a tensioned spring 54 is secured between rod 42 and sta tionary member 56.

Storage and retrieval of information from a selected track of drum 18 is initiated by supplying an input signal to coil 52. This signal produces a magnetic field which moves armature 46 to the left and into contact with core 50. This movement causes cam 28 to slide to the left (to the position indicated by the broken line), resulting in the movement of roller 20 first into contact with and then up inclined section 36 of cam 28 to a position on section 34 of cam 28. Cams 22 and 30 now are rotated, by supplying an appropriate signal to motor 25, to a position which situates roller 20 adjacent the step 21 that will position head 18 adjacent the selected track when roller 20 is in contact with this step of cam 22. Since roller 20 is supported now by cam 28 which is in turn supported by the spiral surface 31 of cam 30 which, as previously mentioned, has the same angular rate of change of radial distance as cam 22, roller 20 is retained out of contact with cam 22 during rotation of cams.22 and 30. When the rotation of cams 22 and 30 is completed, coil 52 is de-energized whereby, through the action of tensioned spring 54, armature 46, rod 42 and cam 28 are moved to the right and into their original positions (solid lines). As cam 28 moves to the right, roller 20 moves down inclined section 36 of cam 28 and into contact with the desired step of cam 22, thereby situating transducer head 10 adjacent the selected track on drum 18. To prevent excessive wearing of the steps 21 by roller 20, inclined section 36 is shaped such that roller 20 contacts steps 21 softly.

From the foregoing it is apparent that placement of transducer head by shaft member 12 adjacent a selected track of drum 18 is not dependent upon rotation of earns 22 and 30 to an exact position. If the rotation of earns 22 and 30 situates roller 20 on any portion of the surface of a selected step 21, transducer head 10 will be positioned adjacent the track on drum 18 corresponding to that step. Accordingly, accurate positioning of transducer head 10 can be achieved by the apparatus of the present invention without costly closed-loop servo systems. Since the configuration of cam 22 is solely determinative of the position of transducer head 10 adjacent drum 18, only cam 22 need be held to close manufacturing tolerances.

While the invention has been described with reference to a particular embodiment thereof, various modifications can be made without departing from the invention. For example, the movement of roller 20 can be controlled by sandwiching stepped cam 22 between two identical spiral cams and by making cam 28 U-shaped. In this embodiment, each leg of the U-shaped cam would be supported by one of the spiral cams. Moreover, the entire upper surface of cam 28 could be inclined to provide for lifting of shaft member 12. Alternatively, the upper surface of cam 28 could be made flat and the bottom surface of cam 28 could be sculptured to provide for the requisite lifting of shaft member 12. Accordingly, I desire the scope of myinvention to be limited only by the appended claims.

I claim:

1. A shaft positioning assembly comprising a first cam having a spiral surface, a second cam having a stepped surface, said first and second cam being mounted unitarily on the drive shaft of a stepping motor, a substantially rectangular cam slidably carried at one end by said spiral surface, the surface of said rectangular cam not in contact with said spiral surface having first and second horizontal sections which define different planes and an inclined section, a spring loaded shaft member having a roller at one end thereof, said roller normally being in contact with said stepped surface, first means for driving the rectangular cam in one direction such that said roller ascends said inclined section of said rectangular cam and is positioned on one of said horizontal sections, and second means for driving the rectangular cam in the opposite direction such that said roller descends said inclined plane and is positioned on said stepped surface.

2. The apparatus according to claim 1 wherein said spiral surface has about the same angular rate of change of radial distance as said stepped surface.

3. Shaft positioning apparatus comprising a first cam having a spiral surface, a second cam having a stepped surface, means for supporting said cams, a shaft member having one end normally supported by a step of said stepped surface, the particular step supporting said shaft member determining the position of said shaft member, an interposer cam having a non-uniform height, said interposer being supported slidably by said spiral surface, means coupled to said interposer cam for sliding said interposer cam into either a first position or a second position, said interposer cam having a greater height measured in the axial direction of said shaft member when in said first position, the curvature of said spiral surface is fixed so that said interposer cam will lift said end of said shaft member from said stepped surface when said interposer cam is in said first position and return said end of said shaft member to said stepped surface when said interposer cam is in said second position.

4. The apparatus according to claim 3 wherein said spiral surface has about the same angular rate of change of radial distance as said stepped surface.

5. Shaft positioning apparatus comprising a first cam having a spiral surface, a second cam having a stepped surface, a drive shaft for supporting said first and second cams, said spiral surface having about the same angular rate of change of radial distance as said stepped surface, a shaft member having one end normally 11'1 contact with said stepped surface, an 111- terposer cam having first and second sections of different height, first means including a rod member coupled to said interposer cam, a solenoid having its armature connected to said rod member, and a spring for sliding said interposer cam into either a first position or a second position, said interposer cam lifting said shaft member from said stepped surface when in said first position but not when in said second position, said first and second cams being positioned on said drive shaft such that the radial distance in any direction from the center of said drive shaft to said stepped surface of said second cam is both (1) greater than the sum of the height of said first section of said interposer cam and the radial distance in that direction from said center of said drive shaft to said spiral surface of said first cam and (2) less than the sum of the height of said second section of said interposer cam and the radial distance in that direction from said center of said drive shaft to said spiral surface of said first cam.

6. The apparatus of claim 5 wherein said shaft member'includes a roller at said one end which is held in contact with said stepped surface by a compressed spring. 

1. A shaft positioning assembly comprising a first cam having a spiral surface, a second cam having a stepped surface, said first and second cam being mounted unitarily on the drive shaft of a stepping motor, a substantially rectangular cam slidably carried at one end by said spiral surface, the surface of said rectangular cam not in contact with said spiral surface having first and second horizontal sections which define different planes and an inclined section, a spring loaded shaft member having a roller at one end thereof, said roller normally being in contact with said stepped surface, first means for driving the rectangular cam in one direction such that said roller ascends said inclined section of said rectangular cam and is positioned on one of said horizontal sections, and second means for driving the rEctangular cam in the opposite direction such that said roller descends said inclined plane and is positioned on said stepped surface.
 2. The apparatus according to claim 1 wherein said spiral surface has about the same angular rate of change of radial distance as said stepped surface.
 3. Shaft positioning apparatus comprising a first cam having a spiral surface, a second cam having a stepped surface, means for supporting said cams, a shaft member having one end normally supported by a step of said stepped surface, the particular step supporting said shaft member determining the position of said shaft member, an interposer cam having a non-uniform height, said interposer being supported slidably by said spiral surface, means coupled to said interposer cam for sliding said interposer cam into either a first position or a second position, said interposer cam having a greater height measured in the axial direction of said shaft member when in said first position, the curvature of said spiral surface is fixed so that said interposer cam will lift said end of said shaft member from said stepped surface when said interposer cam is in said first position and return said end of said shaft member to said stepped surface when said interposer cam is in said second position.
 4. The apparatus according to claim 3 wherein said spiral surface has about the same angular rate of change of radial distance as said stepped surface.
 5. Shaft positioning apparatus comprising a first cam having a spiral surface, a second cam having a stepped surface, a drive shaft for supporting said first and second cams, said spiral surface having about the same angular rate of change of radial distance as said stepped surface, a shaft member having one end normally in contact with said stepped surface, an interposer cam having first and second sections of different height, first means including a rod member coupled to said interposer cam, a solenoid having its armature connected to said rod member, and a spring for sliding said interposer cam into either a first position or a second position, said interposer cam lifting said shaft member from said stepped surface when in said first position but not when in said second position, said first and second cams being positioned on said drive shaft such that the radial distance in any direction from the center of said drive shaft to said stepped surface of said second cam is both (1) greater than the sum of the height of said first section of said interposer cam and the radial distance in that direction from said center of said drive shaft to said spiral surface of said first cam and (2) less than the sum of the height of said second section of said interposer cam and the radial distance in that direction from said center of said drive shaft to said spiral surface of said first cam.
 6. The apparatus of claim 5 wherein said shaft member includes a roller at said one end which is held in contact with said stepped surface by a compressed spring. 